1. Field of the Invention
The present invention relates to lighting technology and more particularly, to a light bulb, which comprises a first circuit board with upward-facing LEDs and a second circuit board with downward-facing LEDs, a metal holder plate set between the first circuit board and the second circuit board to support a light-transmissive shade and a light transmitting lamp shell and to dissipate heat.
2. Description of the Related Art
Since the invention of a first practical electric light bulb by Thomas Alva Edison (Feb. 11, 1847-Oct. 18, 1931), the use of electric light bulb has more than one hundred years of history. An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light which produces light with a tungsten filament wire heated to a high temperature by an electric current through it, until it glows. A tungsten filament-based electric light bulb throws light in an omnidirectional manner, i.e., in all directions. Thus, it quickly replaces conventional dangerous candles and kerosene lamps. Nowadays, many different omnidirectional brilliant light sources are commercially available.
However, tungsten filament-based electric light bulbs consume a large amount of power during operation. It has a low luminous efficacy, i.e., less units of lumens per watt (lm/W). Nowadays, many energy-saving light sources have been created and are intensively used to replace conventional tungsten filament-based electric light bulbs.
The most popularly accepted energy-saving light is a compact fluorescent lamp, also called compact fluorescent light and compact fluorescent tube, designed to replace an incandescent lamp. An energy-saving light of this kind uses a tube which is curved or folded to fit into the space of an incandescent bulb, and a compact electronic ballast in the base of the lamp. Under same illumination conditions, an energy-saving light consumes less electric energy than a conventional tungsten filament-based electric light bulb. However, when compared to a T5 fluorescent lamp, a ballast-based energy-saving light consumes much electric energy.
Conventional energy-saving lights still has drawbacks. At first, an energy-saving light generates small amount of magnetic waves (4.67 milligauss) and microwaves (3.3 μW/cm2 per every watt) during operation. Further, an energy-saving light does not allow light intensity adjustment. Further, an energy-saving light contains a small amount of toxic mercury. Delivery of energy-saving lights or disposing of used energy-saving lights must be carefully handled.
Further, LED lights draw less energy, which makes them more cost effective to use. Many light fixture manufacturers create LED lights for illumination. LED lights are more rugged and damage-resistant than compact fluorescents and incandescent bulbs; however, they are very heat sensitive. Excessive heat or inappropriate applications dramatically reduce both light output and lifetime of LED lights. Further, LED lights are directional. For illumination application, heat dissipation and light dispersion must be properly designed.
A conventional LED light bulb is known comprising a heat sink disposed at the bottom side, a circuit board mounted at the top side of the heat sink, a plurality of light-emitting diodes installed in the circuit board, and a transparent or translucent lamp shell covering the circuit board and the light-emitting diodes. According to this design of LED light bulb, the light-emitting diodes face upward (forward). Due to limited light-emitting angle, a LED light bulb of this design is normally used with a reflector that is mounted around the lamp socket holding the LED light bulb. However, because the light-emitting diodes are directional, the reflector cannot reflect much light rays toward the desired direction. Further, the simple heat sink design cannot effectively and rapidly dissipate waste heat from the light-emitting diodes during the operation of the LED light bulb.